1. Field
This disclosure is generally related to a passive optical network (PON). More specifically, this disclosure is related to transporting a time-division-multiplexing (TDM) clock over a PON.
2. Related Art
IP (internet protocol)-based traffic and TDM-based traffic co-exist on today's networks. Although IP is already pervasive throughout the telecommunications industry, demand for TDM cannot be ignored by service providers.
One driving force for such demand is the corporate-connectivity market, which provides connectivity services to businesses. Note that “Business Services” include voice as well as data, and although voice-over-IP (VoIP) is becoming more important, a significant portion of the corporate-connectivity market will continue to rely on TDM circuits to connect enterprise PBXs (private branch exchange) with IXCs (interexchange carriers) and LECs (local exchange carriers).
Mobile broadband, on the other hand, is growing at an even faster rate, doubling year-over-year through year 2012, due to the increase in laptop Internet traffic and enhanced cellular services, such as web browsing and video distribution. TDM also plays an important role in cellular/mobile backhaul networks. FIG. 1 presents a diagram illustrating a conventional cellular/mobile backhaul architecture (prior art). A cellular/mobile backhaul network 100 includes a RAN (radio-access-network) network center 102, a PSTN (public switched telephone network) 104, a service provider central office 106, and a number of cellular base stations including base stations 108-112. Base stations 108-112 communicate with base station controllers located in central office 106. For example, base station 108 communicates with the corresponding base station controller via link 114. Base station controllers are responsible for aggregating voice and data traffic and maintaining timing and other management synchronizations. Traditionally, the communication between base stations and base station controllers is carried over TDM leased lines, such as a DS0/E1 circuit.
To support the increasing number of subscribers and increasing bandwidth requirements per subscriber, mobile carrier need to increase the bandwidth capacity of their backhaul networks including link 114. A mobile/cellular backhaul network provides connectivity between base stations and base station controllers located at the central office, and carries various types of traffic, including voice traffic (can be either TDM-based voice traffic or VoIP), IP-based data traffic, management signaling traffic, and base station synchronization signals. To solve such a problem, one approach is to increase a mobile backhaul network's capacity by adding more TDM leased lines between the base stations and the base station controllers. However, these TDM circuits are quite expensive. Another approach is to move data traffic (e.g., high-speed downlink packet access (HSDPA) traffic) to a lower cost alternative, such as DSL (digital subscriber line) or cable modem, while continuing to carry voice/cell synchronization traffic over the TDM line. However, most deployed base stations have no capability of separating voice/data traffic to support such an approach. What is needed is a solution that can support TDM-based traffic while providing higher bandwidth at a lower cost